Oligonucleotide analogs having cationic intersubunit linkages

An oligomer comprising a sequence of morpholino subunits, each morpholino subunit comprising a base-pairing moiety, such that the oligomer can bind in a sequence-specific manner to a target nucleic acid, wherein the morpholino subunits are each joined by a phosphorus-containing intersubunit linkage having the structure:

• wherein:
• W is S or O;
• X is NR1R2 or OR6;
• Y is O or NR7;
• and the intersubunit linkage is, at each occurrence, independently:
• linkage (a), where each of R1, R2, R6 and R7 is independently hydrogen or lower alkyl;
• or
• linkage (b1), where X is NR1R2, Y is O and NR1R2 is a piperazino group, such that R1R2 is —CHRCHRN(R3)(R4)CHRCHR—, wherein:
• each R is, at each occurrence, independently H or CH3;
• R4 is H, CH3 or an electron pair;
• and
• R3 is H, lower alkyl, —C(═NH)NH2, —Z-L-NHC(═NH)NH2 or —[C(O)CHR′NH]mH, where Z is carbonyl (C(O)) or a direct bond, L is an optional linker up to 18 atoms in length comprising alkyl, alkoxy or alkylamino groups, or combinations thereof, R′ is a side chain of a naturally occurring amino acid or a one- or two-carbon homolog thereof, and m is 1 to 6;
• and at least one intersubunit linkage is linkage (b1).